Stored energy system for driving a turbine wheel

ABSTRACT

Improved control over the production of motive gas applied by a nozzle (16) to a turbine wheel (10) may be achieved by a method of (a) supplying fuel to a combustor (20), (b) simultaneously with the performance of step (a), supply insufficient oxidant for the fuel through a path (90) to the combustor (20), and (c) simultaneously with steps (a) and (b), supplying additional oxidant sufficient to effect desired combusiton of the fuel to the combustor (20) via a path (92) and at a variable rate.

FIELD OF THE INVENTION

This invention relates to so-called stored energy systems wherein storedfuel and oxidant are combusted to provide motive gases to drive aturbine wheel as in starting or operating an auxiliary power unit or anemergency power unit.

BACKGROUND OF THE INVENTION

Both commercial and miliary aircraft typically carry auxiliary powerunits (APU) and often additionally may utilize a so-called emergencypower unit (EPU) In some instances, the functions of both are combined.

In emergency systems, EPUs, or APUs that operate additionally as EPUsmust be brought into full operational capacity in a relatively shortperiod of time, such as two or three seconds. In the usual case, thesesystems employ a turbine wheel for driving emergency power sources suchas an electrical generator, hydraulic pump or both so as to provide theenergy necessary to continue to operate the aircraft. Consequently, itis necessary that the turbine wheel be accelerated up to normaloperating speed in a relatively short period of time so that if an APUis being utilized to provide emergency power, it can reach a selfsustaining speed. Where an EPU is being utilized, it still must beaccelerated rapidly and then its operation maintained for somepredetermined time period.

Typically, these systems include a storage source for fuel and a highpressure storage vessel for oxidant which is utilized to combust thefuel. The oxidant may be air, oxygen enriched air, or even molecularoxygen.

Because of volume and weight constraints typically associated withaircraft, it is desirable to make the storage vessels as small and aslightweight as possible and that in turn means that it is desirable tohold oxidant requirements for a given emergency operation to a minimum.One way, of course, to minimize oxidant consumption, and thus the needfor oxygen storage volume, is to control the flow of oxidant to acombustor where it is employed to combust fuel to provide motive gasesfor the turbine wheel, so as to provide only the amount of oxidantrequired to effect the desired combustion Consequently, in an EPU, forexample, it will be desirable to sense the power demand of the aircraftwhich is being placed on the turbine wheel of the EPU and regulate theflow of both fuel and oxidant appropriately.

This invention is intended to provide a means whereby improved flowcontrol of oxidant in an EPU or an APU may be obtained.

SUMMARY OF THE INVENTION

It is the principal object of the invention to provide a new andimproved stored energy system. More specifically, it is an object of theinvention to provide both method and apparatus for achieving improvedcontrol over the flow of oxidant to a combustor in a stored energysystem.

According to one facet of the invention, there is provided a turbinewheel adapted to rotate about an axis along with a nozzle in proximityto the turbine wheel for directing motive gases there against. Acombustor is provided and has an outlet connected to the nozzle. Meansare included for directing fuel into the combustor and there is furtherprovided an oxidant storage vessel having an outlet. An oxidant flowline interconnects the storage vessel and the oxidant inlet and includesbranches in fluid parallel with one another with one of the branchesbeing constructed and arranged to provide substantially constant flowand the other of the branches being constructed and arranged to provideselectively variable flow.

In a preferred embodiment, a pressure controlling valve is locatedbetween the vessel outlet and the branches and preferably is a pressureregulator.

The invention contemplates the provision of a fluid flow control valvein the branch constructed and arranged to provide selectively variableflow. Through the use of the system, the entire "turn down" range of thevalve is employed to vary only part of the flow of oxidant so as toenable finer and more precise control of the flow rate within the rangeof normal operating conditions.

The invention also contemplates the provision of a choked orifice in theconstant flow branch and a venturi in the variable flow branch.

According to another facet of the invention, there is provided a methodof controlling the production of motive gas for application to a gasturbine wheel which includes the steps of (a) supplying fuel to acombustor, and (b) simultaneously with the performance of step (a),supplying oxidant to the combustor via two parallel flow paths whileholding flow in one of the paths essentially at a constant rate whilecontrolling flow in the other of the paths to achieve the desiredproduction of motive gas.

In a preferred embodiment, step (b) is performed utilizing a chokedorifice in the one flow path and using a flow varying valve in the otherflow path.

The invention contemplates performing step (b) such that the mass flowrate in the other path ranges from about 45% to about 500% of the massflow in the one path, and preferably, during normal operation of the gasturbine wheel, the mass flow in the other path is at least twice themass flow in the one path.

Other objects and advantages will become apparent from the followingspecification taken in conjunction with the accompanying drawing.

DESCRIPTION OF THE DRAWING

The Fig. is a schematic of a stored energy system made according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An exemplary embodiment of a stored energy system made according to theinvention is illustrated in the drawing in the environment of an EPU.However, it should be understood that the invention is applicable toAPUs as well.

With reference to the drawing, a gas turbine wheel 10 is seen to bemounted on a shaft 12 to be rotatable about the axis defined thereby Theshaft 12 in turn is connected to a power unit 14 which may include anelectrical generator, one or more hydraulic pumps, etc., which provideelectrical or hydraulic energy for loads (not shown).

A nozzle is shown schematically at 16 in proximity to the turbine wheel10 for directing motive gases against the same. The nozzle 16 isconnected to the outlet 18 of a combustor, generally designated 20, toreceive motive gases, including gases of combustion, therefrom.

The combustor includes a first fuel inlet 22 remote from the outlet 18and a second fuel inlet 24 in proximity to the outlet 18 Also includedis an oxidant inlet 26.

Fuel is provided to the inlets 22 and 24 from a fuel tank 28 as will beseen. The fuel tank 28 includes an internal bladder and a pressurizinginlet 32 connected to a source 34 of air under pressure via a controlvalve 36. When the valve 36 is opened, the bladder 32 will bepressurized to expel fuel from the tank 28 via an outlet 38. The fuelsystem also includes a relief valve 40 and a fill port 42 on the inletside of the fuel tank 28.

The outlet 38 is connected to a vent cap 44 as well as a fill port 46and a filter indicator 48. A fuel flow line 50 extends from the filterindicator to a primary fuel flow control servo valve 52 and to asecondary fuel flow control servo valve 54. The valve 52 is connectedvia a shut off valve 56 and an orifice 58 to the first inlet 22 whilethe valve 54 is connected via a shut off valve 60 to the second fuelinlet 24. As can be seen, the valves 58 and 60, when not establishingfluid communication from the valves 52 and 54 to the combustor 24 haveconnections to the source 34 which operate to purge the respective lineto prevent residual fuel from gumming up the fuel lines over a period oftime.

The fuel injected into the combustor 20 at the first inlet 22 iscombusted with oxidant received at the inlet 26 to provide hot gases ofcombustion. Fuel injected into the combustor outlet 18 by the secondinlet 24 does not appreciably participate in the combustion process, ifat all. Rather, the same is vaporized and/or thermally cracked by thehot gases of combustion resulting from fuel introduced at the inlet 22to increase the volume and mass flow of the motive gases being appliedto the turbine wheel 10 by the nozzle 16.

The source 34 may also be connected to an air atomization valve 62 whichin turn is connected to the first inlet 22 to provide for airatomization of fuel thereat and to a purge line 64 for directing apurging flow the combustor when fuel is not being flowed thereto. Alsoincluded is an ignitor 66.

The oxidant system includes a pressure vessel 70 which may be chargedwith an oxidant such as air, oxygen enriched air or even molecularoxygen in some instances. Charging is accomplished through a fill port72 and fill valve 74. A pressure transducer 76 for monitoring thepressure of the charge of oxidant within the vessel 70 is also providedas is a pressure relief valve 78.

A line 80 extends from the outlet 82 of the vessel 70 to a shut-offvalve 84. Downstream of the shut-off valve is a pressure regulator 86which provides, when the shut-off valve 84 is opened, oxidant to ajunction 88 at constant pressure.

The oxidant flow line branches at the junction 88 into a first branch 9and a second branch 92. The branches 90 and 92 rejoin at a junction 94which in turn is connected to the oxidant inlet 26.

The branch 90 is constructed and arranged so as to achieve a constantmass flow rate through the branch 90. This is achieved through the useof a choked orifice 96 within the branch 90. As is well-known, a chokedorifice is sized so that flow through the same, for a given upstreampressure, will be constant regardless of variations in the downstreampressure.

The branch 92 includes an oxidant flow control servo valve 98 in serieswith a venturi 100. The venturi 100 also acts as a choked orifice butminimizes flow losses in the branch 92. A pressure transducer 102 and atemperature transducer 1 4 may also be connected to the branch 92between the servo valve 98 and the venturi 100. The servo valve isoperable to vary the flow through the branch 92 to achieve desiredcombustion conditions within the combustor 20 in response to signalsreceived from a known servo control system 106. The signals are receivedon a line 108 and position feedback information is provided on a line110.

Lines 112 and 114 respectively connect the temperature transducer 104and pressure transducer 102 to the servo control and a line 116 connectsa speed sensor 118 associated with the shaft 12 to the servo control.The valves 52 and 54 are respectively connected to the servo control 106by means of lines 120 and 122. Thus, loading on the turbine wheel 10 maybe determined by determining shaft speed sensed by the sensor 116 andinformation to that effect provided to the servo control to vary fuelflow through the valves 52 and 54 as well as oxidant flow through thevalve 98 as appropriate. Pressure variations as well as the effect onvarying temperature on mass flow rate may be determined through use ofthe transducers 102 and 104 to provide suitable control information.

In one system made according to the invention, the components were sidedto provide 0.056 pounds per second of oxidant through the branch 90while varying the oxidant flow through the branch 92 from 0.026 up to0.28 pounds per second. The very low flow rates through the branch 92are used only during minimum load operation. During normal operation,more typical flow rates through the branch 92 would be in the range of0.12 to 0.28 pounds per second. Thus, the flow rate in the branch 92 mayvary from about 45% all the way up to 500% of the mass flow through thebranch 90 over the entire range of conditions while, in normal operatingconditions, the flow through the branch 92 would be at least twice theflow through the branch 90.

The invention enables the use of a smaller valve 98 than would berequired if all flow were passed through the same. Thus, the cost andweight may be reduced.

More importantly, because the full turn down value of the valve 98 isemployed only on part of the oxidant flow, the total oxidant flow may beregulated with greater precision within the flow rate range for thebranch 92. This not only enhances the combustion process, but improvesthe ability to minimize oxidant storage requirements.

In some instances, it might be desirable to provide in the line 90 somesort of means of compensating for temperature differences to assureconstant mass flow irrespective of the temperature of the oxidantflowing therethrough. However, where oxidant flow through the branch 92is substantially greater than that through the branch 90 as in theforegoing specific example, the effect of temperature variation on flowthrough the branch 90 is insignificant, thereby allowing one to dispensewith any need for temperature compensation in flow through the branch90.

I claim:
 1. A stored energy system for providing hot gases to drive aturbine wheel comprising:a turbine wheel adapted to rotate about anaxis; a nozzle in proximity to said turbine wheel for directing motivegases thereagainst; a combustor having an outlet connected to saidnozzle; means for directing fuel into said combustor; an oxidant storagevessel having an outlet; a pressure controlling valve on said vesseloutlet; an oxidant inlet to said combustor; a first fluid flow path,including a choked orifice, extending from said pressure controllingvalve to said oxidant inlet; and a second fluid flow path including afluid flow control valve extending from said pressure controlling valveto said oxidant inlet
 2. The stored energy system of claim 1 whereinsaid second fluid flow path includes a venturi.
 3. The stored energysystem of claim 1 wherein said combustor has first and second fuelinlets, one remote from said combustor outlet and the other in proximityto said combustor outlet.
 4. A stored energy system for providing hotgases to drive a turbine wheel comprising:a turbine wheel adapted torotate about an axis; a nozzle in proximity to said turbine wheel fordirecting motive gases thereagainst; a combustor having an outletconnected to said nozzle; means for directing fuel into said combustor;an oxidant storage vessel having an outlet; an oxidant inlet to saidcombustor; and an oxidant flow line interconnecting said storage vesseland said oxidant inlet, said flow line including branches in fluidparallel with one of the branches being constructed and arranged toprovide substantially constant flow and another of said branches beingconstructed and arranged to provide selectively variable flow.
 5. Thestored energy system of claim 4 further including a pressure regulatorin said flow line and located between storage vessel and said onebranch.